The objective of this application is to elucidate the early cellular triggers of MAP2 degradation following in vitro ischemia in the rat hippocampal slice. MAP2 is a pivotal cytoskeletal protein that is degraded rapidly after ischemia and may play a key role in the irreversible morphological damage in neurons, leading ultimately to neurodegeneration. The earliest timepoint of MAP2 degradation will be determined and the spatiai location within the neurons where this occurs will be discerned. The role of NNDA and inetabotropic glutamate receptors and the role of calcium will be examined as possible triggers of the MAP2 breakdown. The source of damaging calcium will be identified using confocal laser scanning microscopy and calcium pathway blockers. The roles of calcineurin and calpain as the enzymes responsible for the MAP2 breakdown will be elucidated by measuring MAP2 levels using immunoblotting techniques and calpain inhibitors. The precise location of altered phosphorylation on MAP2 will be identified using MALDI-TOF mass spectrometry and the role of the phosphatase calcineurin in that dephosphorylation will be assayed using specific inhibitors of this enzyme. The results from this project will provide important new information about the mechanism of damage to this key cytoskeletal protein and will further the goal to understand how damage to the cytoskeleton is involved in cell death after stroke.